On Fri, Sep 27, 2013 at 06:35:31AM -0700, Mike Dunn wrote:

On 09/26/2013 05:50 AM, Thierry Reding wrote:

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On Thu, Sep 26, 2013 at 03:26:13PM +0300, Tomi Valkeinen wrote:

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On 26/09/13 15:02, Thierry Reding wrote:

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On Thu, Sep 26, 2013 at 01:13:18PM +0300, Tomi Valkeinen wrote:

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On 11/09/13 14:40, Mike Dunn wrote:

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On 09/10/2013 10:21 AM, Thierry Reding wrote:

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Do you have a real setup that actually needs multiple GPIOs? Usually
such a setup requires some kind of timing or other additional constraint
which can't be represented by this simple binding.

Looking at the Palm Treo code it seems like the reason why multiple
GPIOs are needed is because one is to enable the backlight, while the
other is in fact used to enable the LCD panel. 

There are actually four GPIOs involved!  (There is an embarrasingly horrible
hack in arch/arm/mach-pxa/palmtreo.c that handles the others.)  One is almost
certainly simply backlight power.  The other three are probably LCD related.

When you say "power", do you mean the gpio enables a regulator to feed
power to the backlight? If so, wouldn't that be a regulator, not gpio,
from the bl driver's point of view?

Generally speaking, this same problem appears in many places, but for
some reason especially in display. I'm a bit hesitant in adding "free
form" gpio/regulator support for drivers, as, as Thierry pointed out,
there are often timing requirements, or sometimes the gpios are
inverted, or sometimes the gpio is, in fact, a reset gpio, where you'll
assert the gpio for a short moment only.

I sent out another series a few days ago that somewhat obsoletes this
patch. What it does is basically add a single enable GPIO that can be
used to turn the backlight on and off. In a separate patch, support is
added for a power regulator. The combination of both should be able to
cover the majority of use-cases.

But Mike's case required 4 GPIOs? Or can that be reduced to one gpio and
one regulator?

Well, at least for the backlight it only seemed to involve a single
GPIO. The other three were probably related to LCD and therefore not
really suitable for a backlight driver. Traditionally it has been that
the backlight driver handled these things as well (via the callbacks
installed by board setup code). While really they should be handled by a
separate driver (for the LCD).

Yes, this is currently my best guess.  This is reverse-engineered and
unfortunately I'm not yet able to accurately describe my particular use-case.
Probably as wacky as anything you can imagine, Thierry :)

The gpio and regulator patches will probably suffice.  Thierry, can you please
point me to those patches?  I don't see them in your gitorious tree.  If they
were posted to linux-pwm, I missed them; sorry.

I've stumbled across this email and it's not marked as answered, so here
goes: these patches will be part of my pull request for 3.13. They
should now be in my tree, although that's now moved to kernel.org. You
can find it here:

	https://git.kernel.org/cgit/linux/kernel/git/thierry.reding/linux-pwm.git

Thierry